the diversity of cm carbonaceous chondrite parent bodies...

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Geochimica et Cosmochimica Acta 264 (2019) 224–244

The diversity of CM carbonaceous chondrite parentbodies explored using Lewis Cliff 85311

Martin R. Lee a,⇑, Benjamin E. Cohen a, Ashley J. King b, Richard C. Greenwood c

aSchool of Geographical and Earth Sciences, University of Glasgow, G12 8QQ, UKbDepartment of Earth Science, Natural History Museum (London), Cromwell Road, London SW7 5BD, UK

cPlanetary and Space Sciences, Open University, Walton Hall, Milton Keynes MK7 6AA, UK

Received 17 May 2019; accepted in revised form 14 July 2019; available online 23 July 2019

Abstract

Lewis Cliff (LEW) 85311 is classified as a Mighei-like (CM) carbonaceous chondrite, yet it has some unusual propertiesthat highlight an unrealised diversity within the CMs, and also questions how many parent bodies are sampled by the group.This meteorite is composed of rimmed chondrules, chondrule fragments and refractory inclusions that are set in a fine-grainedphyllosilicate-rich matrix. The chondrules are of a similar size to those in the CMs, and have narrow fine-grained rims. LEW85311 has been mildly aqueously altered, as evidenced by the preservation of melilite and kamacite, and X-ray diffractionresults showing a low phyllosilicate fraction and a high ratio of cronstedtite to Fe, Mg serpentine. The chemical compositionof LEW 85311 matrix, fine-grained rims, tochilinite and P-rich sulphides is similar to mildly aqueously altered CMs. LEW85311 is enriched in refractory elements and REEs such that its CI-normalised profile falls between the CMs and CVs,and its oxygen isotopic composition plots in the CV-CK-CO field. Other distinctive properties of this meteorite includethe presence of abundant refractory inclusions, and hundreds of micrometer size objects composed of needle-fibre calcite.LEW 85311 could come from part of a single CM parent body that was unusually rich in refractory inclusions, but more likelysamples a different parent body to most other members of the group that accreted a subtly different mixture of materials. Themineralogical and geochemical evolution of LEW 85311 during subsequent aqueous alteration was similar to other CMs andwas arrested at an early stage, corresponding to a petrologic subtype of CM2.7, probably due to an unusually low proportionof accreted ice. The CM carbonaceous chondrites sample multiple parent bodies whose similar size and inventory of accretedmaterials, including radiogenic isotopes, led to a comparable post-accretionary evolution.� 2019 The Authors. Published by Elsevier Ltd. This is an open access article under the CC BY license (http://creativecommons.org/licenses/by/4.0/).

Keywords: Carbonaceous chondrite; parent body; oxygen isotopes; refractory inclusions; aqueous alteration

1. INTRODUCTION

The Mighei-like (CM) meteorites are primitive rocksthat are rich in water and organic molecules and so are par-ticularly important for understanding the potential forvolatiles to have been delivered to the terrestrial planetsby asteroids and comets (Alexander et al., 2012). CMs have

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0016-7037/� 2019 The Authors. Published by Elsevier Ltd.

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⇑ Corresponding author.E-mail address: [email protected] (M.R. Lee).

spectroscopic affinities to the �13% of classified asteroidsthat belong to the C-complex (DeMeo et al., 2009;Cloutis et al., 2011). The C-complex includes B, C, Cb,Cg, Cgh and Ch types, which are most common in the outerpart of the main asteroid belt, and �60% of them havespectroscopic signatures of hydrated silicates (Burbine,2017). Current exploration of the near-Earth asteroidsBennu and Ryugu will greatly enhance our understandingof the links between carbonaceous chondrites and their par-ent bodies. Bennu is a B-type asteroid with a hydrated sur-face and has spectroscopic affinities to the highly aqueously

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M.R. Lee et al. /Geochimica et Cosmochimica Acta 264 (2019) 224–244 225

altered CMs (Hamilton et al., 2019). Reflectance spectra ofthe C-type asteroid Ryugu reveal abundant hydroxyl-bearing minerals, and its closest analogues are the ther-mally/shock metamorphosed carbonaceous chondrites(Kitazato et al., 2019).

The nature and diversity of hydrated carbonaceousasteroids can also be explored by investigating variabilitywithin the CM meteorites as they are the most abundantgroup of carbonaceous chondrites. The CMs are typicallycomposed of chondrules (�20 vol.%) and refractory inclu-sions (�5 vol.%) that are supported in a fine-grainedmatrix (�70 vol.%) (Weisberg et al., 2006). The chondrulesand refractory inclusions characteristically have fine-grained rims (FGRs) (e.g., Metzler et al., 1992). All ofthe CMs have undergone parent body aqueous alteration(e.g., McSween, 1979a,b; Bunch and Chang, 1980;Barber, 1981). Phyllosilicates are the most abundant alter-ation product; they comprise 56–91 vol.% of the bulk rock(Howard et al., 2009, 2011, 2015; King et al., 2017) and arethe main constituent of the matrices and FGRs. The mostreactive of the original components, namely mesostasisglass in chondrules, melilite in refractory inclusions, andamorphous material in the matrix and FGRs, is preservedonly in the most mildly altered CMs including Yamato (Y)791198, Paris, Elephant Morraine (EET) 96029 and JbiletWinselwan (Chizmadia and Brearley, 2008; Hewins et al.,2014; Rubin, 2015; Lee et al., 2016; King et al., 2019).The variability in the degree of aqueous alteration of theCMs must reflect differences between parent body regionsin properties such as: (i) the initial ratio of anhydrousmaterial (silicate, sulphide, metal) to water ice; (ii) proxim-ity to regions of fluid flow (e.g., Palguta et al., 2010); (iii)the duration and/or temperature of alteration, which mayin turn relate to depth in the body or the intensity/fre-quency of collisional processing (Rubin, 2012; Hannaet al., 2015). Members of the CM group could thereforehave been sourced from different locations within a singleparent body (e.g., the more altered CMs could have comefrom deeper in the parent body where temperatures werehigher), or from two or more bodies that may have evolvedin contrasting ways (controlled for example by their size,initial abundance of short-lived radionuclides or shockhistory).

Here we ask whether Lewis Cliff (LEW) 85311 can helpto define the extent of heterogeneity of a single CM parentbody, or provide new insights into the diversity of multiplehydrated carbonaceous chondrite parent bodies with CM-affinities. This meteorite has come to our attention becauseits bulk chemical composition suggests that it is a mildlyaqueously altered CM (Xiao and Lipschutz, 1992;Alexander et al., 2013; Friedrich et al., 2018) whereas itsbulk oxygen isotopic composition indicates that it is ananomalous carbonaceous chondrite (Clayton andMayeda, 1999; Choe et al., 2010). We have therefore under-taken a petrographic, mineralogical, chemical and isotopicstudy of LEW 85311 with a focus on understanding thevariety of materials that were accreted, and the nature ofsubsequent parent body processing. In tandem, we haveanalysed a suite of CMs in order to provide a benchmarkfor interpreting the results from LEW 85311.

2. MATERIALS AND METHODS

2.1. Meteorites studied

LEW 85311 was recovered by ANSMET in 1985, and ispaired with LEW 85306, 85309 and 85312. It has a mass of199.5 g, a weathering grade of Be and a shock stage of S1(Scott et al., 1992; Grossman, 1994). LEW 85311 is classi-fied as CM2 (Antarctic Meteorite Newsletter 2008, vol.31). This study used three polished thin sections (LEW85311,31 (�11 � 14 mm); LEW 85311,39 (�11 � 8 mm);LEW 85311,90 (�9 � 7 mm)) and a 2.921 g chip (LEW85311,84). Fifteen CMs were also studied for comparisonwith LEW 85311. They are listed in Table 1, along withtheir petrologic type (i.e., degree of aqueous alteration) rel-ative to three classification schemes. None of these CMshave undergone significant post-hydration heating(Alexander et al., 2013).

2.2. Scanning and transmission electron microscopy

Each thin section was coated with a thin layer of carbonthen studied using a Zeiss Sigma field-emission scanningelectron microscope (FEG-SEM) operated at high vacuum.The Sigma is equipped with an Oxford Instruments XMaxsilicon-drift energy-dispersive X-ray spectrometer (EDX)operated through Oxford Instruments AZtec/INCA soft-ware. Backscattered electron (BSE) images were obtainedat 20 kV/�1 nA. Point counting was undertaken by travers-ing the thin sections using the stepwise stage movementfunction. The apparent diameters of chondrules and refrac-tory inclusions were determined from BSE images. Theapparent diameter of these objects is expressed as: (longaxis + short axis)/2, where the short axis is the diameterof the chondrule/refractory inclusion taken mid way alongits length. Apparent FGR thickness was calculated as:(chondrule apparent diameter with FGR - chondruleapparent diameter without FGR)/2. X-ray maps wereacquired from entire thin sections and from individualobjects at 20 kV/3 nA and a 1024 � 768 pixel resolution,with the spectra being processed using AZtec. Quantitativechemical analyses were acquired using the Sigma operatedat 20 kV/2 nA, with beam currents monitored using a Fara-day cup. Spectra were acquired for 60 seconds, and quanti-fied using INCA software. Calibration used the followingmineral standards, with typical detection limits (wt.% ele-ment) in parentheses: Na, jadeite (0.10); Mg, periclase(0.06); Al, corundum (0.10); Si, diopside (0.11); P, apatite(0.12), S, pyrite (0.10), Cl, tugtupite (0.12), K, orthoclasefeldspar (0.12); Ca, wollastonite (0.10); Ti, rutile (0.18);Cr, chromite (0.22); Mn, rhodonite (0.25); Fe, garnet(0.26); Ni, Ni metal (0.38). Co was not quantified owingto a peak overlap with Fe.

Electron-transparent foils for transmission electronmicroscopy (TEM) and scanning transmission electronmicroscopy (STEM) were cut and extracted from selectedparts of the thin sections using a FEI duomill FocusedIon Beam (FIB) instrument operated using 30 kV Ga+ ionsand over a range of beam currents during the millingprocess (Lee et al., 2003). Foils were initially milled to a

Table 1Meteorite samples studied.

Meteorite Fall or find/location/year Weathering grade Petrologic (sub)type

Rubin1 Alexander2 Howard3

Allan Hills (ALH) 83100 Find/Antarctica/1983 Be 2.1 1.1 1.2Allan Hills (ALH) 83102 Find/Antarctica/1983 B/Ce 2.1 1.1 1.2Cold Bokkeveld Fall/South Africa/1838 n.a. 2.2 1.3 1.4D’Angelo Bluff (DNG) 06004 Find/Antarctica/2006 B – 1.8 1.7Dominion Range (DOM) 08013 Find/Antarctica/2008 B/C – 1.8 1.5LaPaz Icefield (LAP) 02239 Find/Antarctica/2002 B – 1.7 1.47

Lewis Cliff (LEW) 85311 Find/Antarctica/1985 Be 2.6–2.74 1.96 1.77

MacKay Glacier (MCY) 05230 Find/Antarctica/2005 B – 1.8 –Meteorite Hills (MET) 01075 Find/Antarctica/2001 B – 1.5 1.38

Mighei Fall/Ukraine/1889 n.a. – 1.6 1.4Murchison Fall/Australia/1969 n.a. 2.5 1.6 1.5Murray Fall/USA/1950 n.a. 2.4/2.5 1.5 1.5Nogoya Fall/Argentina/1879 n.a. 2.2 1.1/1.6 1.2/1.4Queen Alexandra Range (QUE) 97990 Find/Antarctica/1997 Be 2.6 1.7 1.6Queen Alexandra Range (QUE) 99355 Find/Antarctica/1999 B 2.3 1.5 –Scott Glacier (SCO) 06043 Find/Antarctica/2006 B/Ce 2.05 1.1/1.2 1.2

– not determined.n.a. not applicable as it is a fall.1 Rubin et al. (2007).2 Alexander et al. (2013).3 Howard et al. (2009, 2011, 2015).4 Tentative classification (Choe et al. 2010).5 This meteorite is a CM1, and so equivalent to CM2.0 of Rubin et al. (2007).6 LEW85312 is paired with LEW 85311 and has petrologic type of 1.8.7 Measured for the present study.8 Lee et al. (2019a,b).

226 M.R. Lee et al. /Geochimica et Cosmochimica Acta 264 (2019) 224–244

thickness of �1 lm, then extracted using an in-situ micro-manipulator and welded to the tines of a Cu grid usingion and electron beam deposited platinum. They were thenmilled to �100 nm thickness and loaded into a double-tiltgoniometer holder. Bright-field images and selected areaelectron diffraction (SAED) patterns were acquired usinga FEI T20 TEM operated at 200 kV. High angle annulardark-field (HAADF) imaging and quantitative X-raymicroanalysis used a JEOL ARM200F field-emissionSTEM operated at 200 keV. For the analyses the ARMwas operated with a 182 pA probe current and spectra wereacquired and processed using a Bruker 60 mm2 SDDEDXspectrometer operating Esprit V2.2 software.

2.3. X-ray diffraction (XRD)

A �85 mg chip of LEW 85311 was powdered using anagate mortar and pestle. Approximately 50 mg of the pow-der was then packed into an aluminium sample well andanalysed using an INEL X-ray diffractometer (XRD) witha curved 120� position sensitive detector (PSD) at the Nat-ural History Museum (NHM), London. Copper Ka1 radia-tion was selected and XRD patterns were collected from themeteorite sample for 16 hours, throughout which time itwas rotated. Standards of all minerals identified (excepttochilinite as we do not have a pure sample) in LEW85311 were analysed for 30 min. Modal mineral abun-dances were determined using a profile-stripping methodthat has now been applied to >30 CM chondrites (e.g.

Howard et al. 2015; King et al. 2017). Briefly, the XRD pat-tern of each mineral standard was scaled to the same mea-surement time as the meteorites (i.e., �32 for 16 h). Thestandard pattern was then reduced in intensity until itmatched the intensity in the meteorite patterns, at whichpoint it was subtracted to leave a residual pattern. Aftersubtracting all of the mineral standards there were zerocounts in the residual, and the fit factors were correctedfor relative differences in X-ray absorption to give theirfinal volume fractions in LEW 85311.

2.4. Oxygen isotopic analysis

Oxygen isotopic analysis of LEW 85311 was undertakenby infrared laser fluorination at the Open University (Milleret al., 1999; Greenwood et al., 2017). When analysing pre-dominantly anhydrous samples it is normal procedure toreduce the system blank by flushing the chamber with atleast two aliquots of BrF5, each held in the chamber for20 min. However, for samples that contain a significantproportion of phyllosilicates, such as CMs, this protocolcan be problematic as it may result in preferential reductionin the hydrated silicate fraction prior to the high tempera-ture fluorination step. This is because phyllosilicates canreact with BrF5 at low temperature during this blank reduc-tion procedure. To minimise this problem, LEW 85311 wasrun in ‘‘single shot” mode, with only one standard and onealiquot of LEW 85311 loaded at a time (Schrader et al.,2014). This involved a four-stage procedure: (1) a 5 min


BrF5 measured blank was run prior to the analysis of LEW85311, (2) a single �2 mg aliquot of the meteorite was thenanalysed, (3) a second 2 min measured blank was conductedafter this analysis and finally (4) the isotopic composition ofthe internal obsidian standard was then measured. Afterfluorination, the O2 gas released was purified by passing itthrough two cryogenic nitrogen traps and over a bed ofheated KBr. The isotopic composition of the purified oxy-gen gas was then analysed using a Thermo Fisher MAT253 dual inlet mass spectrometer (mass resolving power�200). Interference at m/z = 33 by NF+ was monitoredby performing scans for NF2

+ on the sample gas followinginitial analysis. As NF2

+ was below interference levels nofurther sample treatment was required.

Analytical precision (2r) for the Open University sys-tem, based on replicate analyses of an internal obsidianstandard, is ±0.05‰ for d17O; ±0.09‰ for d18O; ±0.02‰for D17O (2r) (Starkey et al., 2016). Oxygen isotopic anal-ysis for LEW 85311 are reported in standard d notation,where d18O has been calculated as: d18O = [(18O/16O)sample/(18O/16O)ref � 1] � 1000 (‰) and similarly for d17O usingthe 17O /16O ratio, the reference being Vienna StandardMean Ocean Water (VSMOW). For the purposes of com-parison with the results of Clayton and Mayeda (1999)D17O, which represents the deviation from the terrestrialfractionation line, has been calculated as:D17O = d17O � 0.52 � d18O.

3. RESULTS

3.1. Bulk chemical and oxygen isotopic composition

Bulk samples of LEW 85311 and LEW 85312 have beenchemically and isotopically analysed by Xiao and Lipschutz(1992), Choe et al. (2010), Alexander et al. (2012, 2013),Friedrich et al. (2018) and Mahan et al. (2018) (Supplemen-tary Table A1). These datasets can be used to assess theaffinity of LEW 85311 to other carbonaceous chondritegroups. The ratio of elements with different volatilities istaxonomically indicative, namely highly volatile (Zn) tomoderately volatile (Mn) and refractory (Sc) (i.e., Sc/Mnand Zn/Mn) (Kallemeyn and Wasson, 1981; Friedrichet al., 2018) (Table 2). Using these ratios, Friedrich et al.(2018) place LEW 85311 within the range of 15 CMs thatthey had also analysed. However, data in Choe et al.(2010) and average Sc/Mn and Zn/Mn values from all of

Table 2Mn, Sc and Zn element composition of LEW 85311 compared to the CM

LEW 853111 LEW 853112 LEW

Sc (lg/g) n.a. 7.6 7.36Mn (lg/g) n.a. 1880 1690Zn (lg/g) 179 151 203Sc/Mn � 1000 (at) – 4.9 5.3Zn/Mn � 100 (at) – 6.8 10.1

n.a. – not analysed.1 Xiao and Lipschutz (1992).2 Choe et al. (2010).3 Friedrich et al. (2018).4 Mahan et al. (2018).

the previous studies plot slightly outside of this range,although still much closer to the CMs than other carbona-ceous chondrite groups (Table 2). The CI-normalised ele-mental composition of LEW 85311 is comparable to Paris(here chosen as representative of a mildly aqueously alteredCM) for elements with 50% condensation temperatures lessthan Nb (1559 K), whereas the more refractory elementsand most REEs plot between Paris and the CV carbona-ceous chondrites (Fig. 1, Supplementary Table A1).

The bulk oxygen isotopic composition of LEW 85311was originally determined by Clayton and Mayeda (1999).They classified LEW 85311 as an ungrouped carbonaceouschondrite (C2) on the basis of its ‘‘exceptional” oxygen iso-tope composition, but noted that ‘‘volatile and labile traceelements in LEW 85311 are typical of CM2 chondrites(Xiao and Lipschutz, 1992).” In addition, the matrix sepa-rate of LEW 85311 that was analyzed by Clayton andMayeda (1999) plots within the CM2 field (Fig. 2), provid-ing evidence for a possible genetic link between LEW 85311and the CMs. The bulk oxygen isotope analysis of LEW85311 undertaken for the present study is richer in 16O thanthat of Clayton and Mayeda (1999) and plots well inside theCV-CK-CO field (Greenwood et al., 2010; Alexander et al.,2018) (Fig. 2, Table 3).

3.2. XRD modal mineralogy

The XRD pattern and modal mineralogy of LEW85311,84 is comparable to the least altered CMs (Table 4).It has a phyllosilicate fraction (PSF) of 0.67 (wherePSF = total phyllosilicate/(total anhydrous silicate + totalphyllosilicate)), corresponding to type 1.7 on the classifica-tion scheme of Howard et al. (2009, 2011, 2015). LEW85311 stands out from those CMs whose modal mineralogyhas been quantified using XRD by virtue of its relativelyhigh abundance of Fe,Ni metal (0.3 vol.%), scarcity of sul-phide (0.5 vol.%), absence of calcite, low PSF and highratio of cronstedtite to Fe, Mg serpentine (Fig. 3).

3.3. Petrography and mineralogy

The constituents of LEW 85311,39 as determined bySEM point counting are (in vol.%, n = 848): matrix(39.9); FGRs (30.7); chondrules, chondrule fragments andrefractory inclusions (29.2) (Fig. 4). Calcite-rich objectscomprise 0.2 vol.%, in agreement with the low abundance

s.

853113 LEW 853124 Average1–4 CMs (n = 15)3

n.a. 7.5 6.99–8.96n.a. 1785 1460–1870155 ± 17 172 171–242– 5.1 5.2–6.5– 8.1 8.6–11.1

Fig. 1. The chemical composition of LEW 85311 normalised to CI (Ivuna) and Fe. The main graph elements are arranged in order of 50%condensation temperature (Lodders, 2003), decreasing to the right. The inset shows REE in Z order, also normalized to CI and Fe. Data fromParis (CM2.7) and the median of three CVs are plotted for comparison. Ivuna, Paris and the CV data are from Braukmuller et al. (2018) (notethat Paris contains lithologies with different degrees of aqueous alteration, but the relationship of the sample analysed to these lithologies isunknown). LEW 85311 data are from Xiao and Lipschutz (1992), Choe et al. (2010), Friedrich et al. (2018) and Mahan et al. (2018)(Supplementary Table A1). An average value has been used where the same element was measured in two or more these studies.

Fig. 2. Bulk oxygen isotopic composition of a subsample of LEW85311,84 analysed in the present study compared to the data ofClayton and Mayeda (1999) (C&M). NWA 5958 (C2-ung) is alsoplotted (Jacquet et al., 2016). TFL – Terrestrial Fractionation Line.CCAM – Carbonaceous Chondrite Anhydrous Mineral. CV-CO-CK data from Greenwood et al. (2010) and Alexander et al. (2018).

Table 3Oxygen isotopic composition of LEW 85311 and NWA 5958(C2-ung).

LEW 85311 NWA 59582

The presentstudy

Clayton andMayeda1

d17O (‰) �5.98 �2.98 �3.25d18O (‰) �2.07 1.21 1.92D17O (‰) �4.90 �3.61 �4.26

1 Clayton and Mayeda (1999, Table 5).2 Mean of 3 analyses (Jacquet et al., 2016).

Table 4Modal mineralogy of LEW 85311,84 (vol.%).

Cronstedtite 37.8Mg-serpentine 27.0Olivine 21.4Enstatite 10.1Sulphate 1.7Magnetite 1.2Fe-sulphide 0.5Metal 0.3Carbonate n.d.Phyllosilicate fraction (PSF) 0.67Cronstedtite/Mg-serpentine 1.40Petrologic type 1.7

Determined by XRD.n.d. – not detected.


of this mineral as revealed by XRD. Table 5 lists pointcounting results from eight CMs for comparison.

3.3.1. Chondrules and chondrule fragments

A previous study of LEW 85311 found that it containsbarred olivine (BO), porphyritic olivine (PO), porphyritic

olivine–pyroxene (POP) and porphyritic pyroxene (PP)chondrules with an average apparent diameter of 190 lm(n = 100) (Choe et al., 2010) (Fig. 5). The 72 chondrulesand chondrule fragments measured for the present studyhave an approximately log-normal distribution (Supple-mentary Fig. A1) with an average apparent diameter of213 ± 153 lm. Chondrule fragments comprise one or sev-eral grains of olivine, pyroxene and/or Fe,Ni metal. Bothintact and fragmented chondrules have FGRs. Fayalitic oli-vine in type II chondrules is very similar in composition toolivine in type II chondrules from Paris (CM) and Acfer094 (C2-ung) (Supplementary Table A2). Olivine andpyroxene grains in intact chondrules are typically pristine,whereas in a few cases grains of fayalitic olivine withinchondrule fragments have been partially replaced by phyl-losilicates along their contact with the enclosing FGR(Fig. 5e and f). No chondrule mesostasis glass has been pre-served, and in its place are pores, porous arrays of pyroxenecrystallites or phyllosilicates (Fig. 5b). Chondrules can alsocontain rounded pores tens of micrometres in diameter(Fig. 5c).

Fig. 3. The modal mineralogy of LEW 85311, as determined byXRD, compared to 36 CMs that have been analysed previously(Howard et al., 2009, 2011, 2015; King et al. 2017). The number ofCMs with an above zero abundance of each mineral is indicated onthe right hand side. Sulphates have not been included as they maybe products of terrestrial weathering (Lee, 1993).


Many type I chondrules contain ‘nuggets’ of kamacite,which have an average composition of Fe94.3Ni5.2Cr0.4 (11analyses from five chondrules) (Fig. 5a). These kamacitegrains have been partially or near-completely altered, and

Fig. 4. BSE image (a) and multi-element X-ray map (Mg red, Al blue, Cachondrules red, refractory inclusions light blue, calcite green, and the matrin this figure legend, the reader is referred to the web version of this arti

Table 5Abundance (vol.%) of the three main constituents of LEW 85311 compa

Objects FGRs Matrix1

LEW 85311 29.4 30.7 39.9DNG 06004 33.7 13.9 52.4DOM 08013 37.0 23.5 39.6MCY 05230 30.0 23.3 46.7QUE 97990 36.1 18.2 45.7LAP 02239 29.3 14.5 56.1MET 01075 14.6 6.5 78.9QUE 99355 20.2 9.9 70.0Cold Bokkeveld 13.5 4.0 82.5

Determined by SEM point counting.Objects are chondrules, chondrule fragments and refractory inclusions.n – number of points counted.1 Includes calcite grains.2 Alexander et al. (2013).

two compositionally and petrographically distinct types ofalteration products are recognized: (i) Fe-rich/S-rich, whichform a narrow rim to kamacite grains and also penetrateinto their interior; (ii) Fe-rich/S-poor, which occur as a con-centrically laminated mantle and veins extending from themantle into the FGR (Fig. 6). The Fe-rich/S-rich materialis dominated by Fe, Ni and S, and gives low analyticaltotals (Table 6). It is compositionally comparable totochilinite that has formed by the alteration of kamacitein CM carbonaceous chondrites (Table 7) (Tomeoka andBuseck, 1985; Palmer and Lauretta, 2011). LEW 85311tochilinite is closer in composition to tochilinite in themildly altered CMs than in the more highly altered mete-orites (Table 7). The Fe-rich/S-poor mantles yield low ana-lytical totals (�79 wt.%) suggesting significantconcentrations of unanalyzed OH/H2O (although other ele-ments such as carbon, and porosity, can also contribute tothe low totals) (Table 6). The detection of Cl suggests thatakaganeite (b-FeOOH) is present. Akaganeite is a commonweathering product of Antarctic iron meteorites and ordi-nary chondrites (Buchwald and Clarke, 1989) where it hasthe following compositional range (wt.%): Fe (39–60), Ni(0.5–19, with 3–5 being typical); Cl (0.3–5.4); S (0–2). Mostanalyses of LEW 85311 Fe-rich/S-poor mantles are withinthe range of Antarctic akaganeite (wt.%): Fe (38–54), Ni

green) (b) of LEW 85311,90. The colour coding of (b) renders type Iix and FGRs dark red. (For interpretation of the references to colorcle.)

red to eight CMs.

Matrix/FGR n Petrologic type2

1.3 848 1.93.8 700 1.81.7 230 1.82.0 180 1.82.5 269 1.73.9 399 1.712.1 403 1.57.1 233 1.520.6 252 1.3

Fig. 5. BSE images of chondrules and chondrule fragments, and their enclosing radially fractured and micropore-rich FGRs. (a) POPchondrule in LEW 85311,31. Between the grains forsterite and enstatite (mid-grey) are small crystals of Ca-rich pyroxene (light grey;En54Wo45Fs1). Nodules of kamacite (white) have been partially replaced by tochilinite (mid-grey). (b) POP chondrule in LEW 85311,31.Between the grains of forsterite and enstatite (mid-grey) are small crystals of Ca-rich pyroxene (En55Wo38Fs7). Dissolution of the mesostasishas left micropores (black) with skeletal crystallites. (c) PO chondrule in LEW 85311,39. Some of the fayalitic olivine crystals are zoned andthe chondrule has a significant internal porosity (black). (d) BO chondrule in LEW 85311,31. The small high-Z grains are Fe-sulphide.Between crystals of fayalitic olivine (Fo25-56) are pyroxenes (En38Wo1Fs61). (e) A grain of fayalitic olivine (Ol) in LEW 85311,39. (f) Detail ofthe contact of fayalitic olivine with its FGR (boxed area in (e)). The olivine has been partially replaced by phyllosilicate (Ph), probablycronstedtite. The high-Z (white) grains are Fe-sulphide.

Fig. 6. BSE images of altered kamacite (K). (a) A grain in LEW 85311,31 enclosed by a FGR. Tochilinite (mid-grey) embays the outer edgesof the kamacite grain and extends into its interior (arrowed). (b) A grain in LEW 85311,39 that has a thick and concentrically laminatedmantle of Fe-rich/S-poor alteration products. Veins of the same material cross-cut the FGR (arrowed).


Table 6Chemical composition (wt.%) of Fe- and S-bearing alteration products in LEW 85311 kamacite grains, calcite-rich objects and veins.

Fe-rich/S-poor Fe-rich/S-rich

Kamacite hosted Kamacite hosted Calcite-rich object hosted Vein hosted

SiO2 0.81 ± 0.61 3.03 ± 0.95 6.31 ± 0.50 5.53 ± 1.46Al2O3 0.12 ± 0.19 0.63 ± 0.15 0.83 ± 0.07 0.68 ± 0.20Cr2O3 1.33 ± 0.76 2.48 ± 1.43 d.l. 2.14 ± 0.33Fe2O3 65.35 ± 4.58 55.14 ± 3.11 58.92 ± 3.96 58.08 ± 1.83NiO 4.45 ± 1.08 8.81 ± 0.85 6.30 ± 0.84 6.23 ± 0.02MgO 0.70 ± 0.48 2.91 ± 0.44 2.19 ± 0.19 2.09 ± 0.21CaO 0.26 ± 0.24 1.33 ± 0.24 1.19 ± 0.48 0.52 ± 0.17Na2O 0.55 ± 0.25 d.l. 0.12 ± 0.10 0.50 ± 0.04P2O5 1.13 ± 0.43 n.a. 1.59 ± 0.58 2.06 ± 0.25Cl 0.69 ± 0.53 n.a. 0.13 ± 0.10 0.24 ± 0.02S 3.97 ± 2.39 16.88 ± 1.68 12.90 ± 0.96 8.17 ± 2.55

Total 79.37 91.56 90.55 86.25n 26 5 15 2

K, Ti and Mn were sought, but below detection limits (d.l.).n.a. – not analysed.± One standard deviation.Individual analyses provided in the supplementary data.

Table 7Chemical composition (atomic) of Fe-rich/S-rich alteration products in kamacite grains from LEW 85311 and four CMs.

Mg/(Mg + Fe) Ni/(Fe + S) Petrologic type3

LEW 85311,311 0.10 ± 0.02 0.10 ± 0.01 1.9Murchison2 0.12 0.12 1.6Murray2 0.12 0.11 1.5Cold Bokkeveld2 0.20 0.09 1.3Nogoya2 0.18 0.05 1.1/1.6

± One standard deviation.1 Mean of five analyses of alteration products in two kamacite grains.2 Palmer and Lauretta (2011, Table 2).3 Alexander et al. (2013).


(2–6), Cl (<0.1–2), S (<0.1–12). The main difference to aka-ganeite in Buchwald and Clarke (1989) is a wider range ofS, although only a few analyses have high S concentrations(Fig. 7). The low Cl values probably reflect an intergrowthof akaganeite with Cl-free goethite (Buchwald andClarke, 1989).

3.3.2. Refractory inclusions

In order to assess the abundance, mineralogy and degreeof preservation of refractory inclusions, those occurring in a0.28 cm2 area of LEW 85311,90 were studied in detail(Fig. 8a–c). This area contains 41 inclusions (146/cm2).They have an apparent diameter of 20–402 lm (average105 ± 88 lm) and an aspect ratio of 1.2–6.5 (average 2.5± 1.2). The mineralogy and structure of all inclusionsoccurring in a 0.08 cm2 part of the mapped region wasdetermined. This area contains 15 inclusions. Seven of themare dominated by spinel and pyroxene (Fig. 8a), four by spi-nel and perovskite (Fig. 8b), and each of the others containsone refractory mineral (spinel, perovskite, pyroxene,gehlenite; Fig. 8c). Most of the inclusions are porous andcontain phyllosilicates (e.g., Fig. 8b); the gehlenite grain

has been partially replaced by coarse grained phyllosilicate(Fig. 8c). Among the 15 inclusions are five morphologicaltypes (after Rubin 2007): five banded, three nodular, twosimple, three simple distended and two complex distended.

In addition to occurring in LEW 85311,90, gehlenite ispresent in a refractory inclusion in LEW 85311,39, whereit is accompanied by spinel, perovskite, pyroxene and Ca-carbonate (Fig. 8d and e). Its empirical formula is Ca2.0Al1.5-Mg0.2Si1.2O7 (average of two analyses). The presence ofpores surrounding the gehlenite, and the occurrence of smallrelict gehlenite grains (Fig. 8e) suggests that it has survivedpartial dissolution. Melilite-bearing refractory inclusionswere also described from LEW 85311 by Simon et al.(2005). They found two inclusions where melilite mantleshibonite, and this relationship was interpreted to show thatthe melilite formed earlier. Although most LEW 85311re-fractory inclusions are comparable in mineralogy and mor-phology to those in the CMs (Rubin et al., 2007), the LEW85311,31 thin section contains a rare forsterite chondruleenclosing a simple spinel-perovskite refractory inclusion(Fig. 8f). Reaction of forsterite with spinel has formed ahigh-Z material that is rich in O, Al, Si, Ca and Ti (Fig. 8f).

Fig. 7. The compositions (at.%) of Fe- and S-bearing phaseshosted in LEW 85311 calcite-rich objects, kamacite grains, a Fe-rich vein and the matrix. All analyses of the material within thecalcite objects, Fe-rich vein, kamacite nuggets and matrix (exceptP-rich sulphide) plot along a line (Fe + S)90-95Ni10-5. The grey ovaldelineates the compositional range of tochilinite after kamacite inCM chondrules (Palmer and Lauretta, 2011). LEW 85311 pent-landite and pyrrhotite data are from Kimura et al. (2011) whereasthe composition of kamacite is from the present study.


3.3.3. Calcite-rich objects

Most LEW 85311 Ca-carbonate occurs as meshworks ofneedle-fibre crystals, which are present in all three thin sec-tions and most abundant in LEW 85311,39. ThisCa-carbonate occurs in two petrographic contexts: (i) small(10 s lm) patches within chondrules and chondrule frag-ments (Fig. 9a–e); (ii) the main constituent of relativelylarge (>�100 lm) rounded, irregular or elongate objectsthat have a FGR (Fig. 10). The needle-fibre crystals wereidentified as calcite by SAED. On average they are�18 lm in length by 2 lm in width. Individual fibres areaggregates of �1 lm wide acicular crystals (Fig. 9d andf). The fibres may be straight or curved, sometimes to suchan extent that they are almost circular (Fig. 9d). Most fibresare oriented randomly relative to each other, althoughthose at the edges of the meshworks may be aligned withtheir long axes roughly parallel to each other in a radiatingor palisade structure (Fig. 9b). TEM shows that the fibreshave a low defect density and no inclusions (Fig. 9f).

In almost all objects the needle-fibre calcite is associatedwith one or more Fe- and Cr-rich minerals (kamacite,Fe-sulphide, schreibersite, P-rich sulphide, eskolaite)(Figs. 9 and 10) (Supplementary Table A3). The kamacitegrains are usually rimmed or cross-cut by Fe-rich/S-richalteration products whose composition is similar totochilinite after kamacite (Table 6). The average formulafor the P-rich sulphides is Fe2.0Ni2.2S3.2P0.8 (normalized toFe = 2; n = 9 analyses), which is similar to P-rich sulphideselsewhere in LEW 85311 that were analysed by Nazarovet al. (2009) (Table 8). Fe-sulphide, schreibersite and esko-laite crystals tend to be present at the margins of the mesh-works, whereas the tochilinite and P-rich sulphide occurwithin them (Figs. 9a, b, e and 10).

3.3.4. Fe-rich veins

Two Fe-rich veins occur in LEW 85311,31 (Fig. 11). Oneis 500 lm in length by 15 lm in width and has a FGR(Fig. 11a). It contains grains of kamacite, Fe-sulphide andschreibersite in a matrix of a Fe-rich/S-rich material thatis comparable in composition to tochilinite after kamacitein LEW 85311 chondrules (Table 5, SupplementaryTable A3). The other vein is partly wrapped around a chon-drule fragment and is composed solely of tochilinite and P-rich sulphide (Fig. 11b).

3.3.5. Matrix and FGRs

LEW 85311 matrix and FGRs yield low analytical totalsthat are consistent with a phyllosilicate-rich mineralogy(Supplementary Table A4). Both components plot withinthe ‘serpentine field’ of a ternary diagram, and specificallybetween end-member serpentine, and LEW 85311 cronst-edtite and tochilinite-cronstedtite intergrowths (TCIs)(Fig. 12). The matrix and FGRs have a lower Mg/(Mg+ Fe) than the bulk meteorite (Fig. 12). Comparison ofLEW 85311 matrix and FGR compositions with 13 CMsalso analysed for the present study show a comparable pat-tern of depletion and enrichment, with LEW 85311 beingcompositionally closest to those CMs that have been mildlyaqueously altered (Supplementary Fig. A2). The MgO/FeOratio of CM matrices is informative about CM parent bodyhistory as it increases with progressive aqueous alteration(McSween, 1987). The value for LEW 85311 (0.33) is lowerthan the CM2.7 meteorite Paris (0.39) (SupplementaryTable A4).

The apparent thickness of FGRs on chondrules andchondrule fragments ranges from 15 to 101 lm (average37 ± 25 lm, n = 72), and is positively correlated with theirdiameter (R2 = 0.73, slope = 0.14) (SupplementaryFig. A3). FGRs have a sharp contact with the matrix andare distinguished from it by a lower Fe/Si ratio (Supple-mentary Table A4) and a finer and more homogeneousgrain size (Fig. 13a). Despite being more compact thanthe matrix, FGRs characteristically contain fractures andmicropores (Fig. 13b). Fractures are typically oriented nor-mal to the outer edge of the host object and pinch outtowards the matrix (Fig. 5). Micropores are an average of6 lm in size and some have a negative crystal shape. Theycan occur throughout the FGR, but are usually more abun-dant closer to the matrix (Fig. 13b). TEM shows that theFGRs contain silicate and sulphide mineral grains of arange of sizes, between which are cylindrical TCI and ser-pentine crystals (Fig. 13c–f).

The matrix contains fine silicate and sulphide grainstogether with clumps of phyllosilicates and rare grains ofCa-carbonate (Fig. 14). Particles �1 lm in size also occurin the matrix that are similar in size and shape to amor-phous domains in Y-791198 (Chizmadia and Brearley,2008) and GEMS grains in Paris (Leroux et al., 2015); theyare thus likely to be composed of amorphous silicate, sul-phide and metal (Fig. 14b). Locally developed petrofabricsare evidence for mild ductile compaction of the matrix(Fig. 11b). TEM and STEM images show that the matrixcontains platy and entangled cylindrical crystals (Fig. 14cand d). The platy crystals have a chemical composition

Fig. 8. Refractory inclusions, with morphology classification from Rubin (2007). (a)-(c) BSE images of inclusions from the area of LEW85311,90 that was studied in detail. (a) A banded spinel (Sp)-diopside (Di) inclusion contained within a FGR. (b) A simple distended spinel-perovskite inclusion with a high microporosity (black). The edge of a chondrule is on the right hand side. (c) A simple inclusion comprising acrystal of gehlenite (Gh) whose edges have been etched and partly replaced by phyllosilicates (Ph). (d) X-ray map overlain on a BSE image of asimple inclusion in LEW 85311,39. The X-ray map has been coloured as follows: Mg light green, Si purple, Ca yellow, Fe light blue. Thiscolouration highlights the main minerals: spinel (Sp, dark green), gehlenite (Gh, orange) and Ca-carbonate (Cc, light green). Part of anotherrefractory inclusion is at the bottom of the image (arrowed). (e) BSE image of the left hand part of the inclusion in (d), highlighting therelationship of gehlenite to spinel and porosity (black). The arrows highlight two small grains of gehlenite. (f) Forsterite (Fo) chondrule inLEW 85311,31 that has a spinel (Sp)-perovskite refractory inclusion at its core. The selvage of high-Z material between the refractoryinclusion and the forsterite (arrowed) is rich in Al, Si, Ca and Ti. (For interpretation of the references to color in this figure legend, the readeris referred to the web version of this article.)


close to that of cronstedtite in Paris (Table 9), and such amineralogy is consistent with their �0.7 nm lattice fringespacing (Fig. 14d). The cylindrical crystals are intermediatein composition between cronstedtite and tochilinite(Table 9) and so are inferred to comprise an intergrowthof both minerals (i.e., type II TCI; Tomeoka and Buseck,1985; Pignatelli et al., 2017). Although TCI has been iden-tified within the matrix by TEM, the tens of micrometer sizeTCI clumps that characterize CM matrices are absent (asalso noted by Choe et al., 2010).

4. DISCUSSION

Our petrographic, mineralogical, chemical and isotopicresults show that LEW 85311 has both similarities anddifferences to the CMs. Below we describe the geological

history of LEW 85311 and evaluate its affinity to the CMgroup through a discussion of the material that wasaccreted, and its subsequent mineralogical and geochemicalevolution. We then consider the implications of theseresults for understanding the nature of its parent body,and specifically whether LEW 85311 comes from the samebody(ies) as other members of the CM group, or is a pieceof a different, and maybe previously unsampled, hydratedC-complex asteroid.

4.1. LEW 85311 geological history

4.1.1. Accreted material

The LEW 85311 parent body was formed by accretionof coarse-grained objects (chondrules, chondrule frag-ments, refractory inclusions), a fine-grained matrix, and

Fig. 9. Calcite-rich objects. (a)-(e) BSE images. (a) A POP chondrule in LEW 85311,31 that has a patch of needle-fibre calcite protruding fromits upper right hand edge. The rounded black areas within the chondrule are pores. (b) The patch of calcite in (a), which comprises a porousmeshwork of fibres. The white crystals that decorate the boundary between the patch and FGR are Fe-sulphide. The mid-grey material in thelower part of the patch is similar in chemical composition to tochilinite after kamacite. (c) An object in LEW 85311,90 that is composed of alarge grain of kamacite (white) and a meshwork of calcite fibres. The object has a thick FGR. (d) The calcite fibres in (c), each of which iscomposed of a sheath of acicular crystals. (e) A shard-shaped calcite object in LEW 85311,39 with a FGR. The inset show that it containssmall relict grains of kamacite (K) and its edges are lined by high-Z minerals including eskolaite (Esk) and schreibersite (Sc). (f) Bright-fieldTEM image of needle-fibre calcite from LEW 85311,39. Some of the fibres are aggregates of acicular crystals.


probably also water-rich ice. The origin of FGRs on thecoarse-grained objects has been debated, with three pro-cesses being proposed: (i) accretion of dust within the solarnebula (e.g., Metzler et al., 1992); (ii) impact compaction offine-grained matrix material around chondrules and otherobjects within the parent body (e.g., Trigo-Rodriguezet al., 2006); (iii) aqueous alteration of the host object(e.g., Sears et al., 1993). Clues to the origin of LEW85311 FGRs come from their structure and composition.They have a sharp outer edge, which separates the compactand equigranular rim material from the more porous andmineralogically heterogeneous matrix. The FGRs also dif-fer in chemical composition to the matrix (SupplementaryTable A4), and their apparent thicknesses correlates wellwith the apparent diameter of their host objects (Supple-mentary Fig. A3). We propose that these properties areinconsistent with an origin by impact compaction, and best

explained by accretion in the solar nebula. This conclusionagrees with results of an X-ray tomography study ofMurchison FGRs by Hanna and Ketcham (2018). Theyalso observed that the FGRs are compositionally uniformacross different chondrule types, thus arguing against anorigin by aqueous alteration of their more compositionallyvariable host objects. Chondrules, chondrule fragments andrefractory inclusions therefore had FGRs when they wereincorporated into the LEW 85311 parent body.

Relative to eight CMs analysed for the present study(Table 5), LEW 85311 contains the second lowest propor-tion of matrix and highest proportion of FGRs. It thussomewhat resembles the ‘primary accretionary rock’ lithol-ogy that characterises unbrecciated CMs (Metzler et al.,1992). The proportion of the meteorite that consists ofchondrules, chondrule fragments and refractory inclusions(29.4%) is close to the CM average (26.8 vol.%) (Table 5).

Fig. 10. BSE image (a) and X-ray element maps (b)–(e) of a calcite-rich object in LEW 85311,31 that is enclosed within a FGR. Calcite (C,mid grey) has been lost from two parts of the object (black), presumably during thin section preparation. The X-ray maps show that P, S, Feand Ni are co-located as grains of P-rich sulphide that are intergrown with calcite.

Table 8Chemical composition (atomic) of P-bearing sulphides in LEW 85311 and six CMs.

S/P (Fe + Ni)/P Fe/Ni Petrologic type3

LEW 853111 3.78 ± 0.22 4.94 ± 0.30 0.94 ± 0.13 1.9LEW 853112 3.82 ± 0.80 5.10 ± 0.68 1.07 ± 0.08 1.9Murchison2 3.36 ± 0.84 4.54 ± 0.80 0.93 ± 0.22 1.6Mighei2 8.75 ± 3.00 9.37 ± 2.92 1.10 ± 0.20 1.6Murray2 3.40 ± 0.52 4.55 ± 0.59 0.85 ± 0.11 1.5Cold Bokkeveld2 9.10 ± 4.14 9.94 ± 4.06 1.20 ± 0.26 1.3Nogoya2 12.40 ± 6.14 13.20 ± 6.01 1.21 ± 0.27 1.1/1.6ALH 831002 24.83 ± 5.88 25.17 ± 5.83 1.81 ± 0.32 1.1

± One standard deviation.Individual analyses for LEW 85311 provided in the supplementary data.1The present study. Ratios calculated from eight analyses of seven grains in LEW 85311,31 and one analysis of one grain in LEW 85311,90.2 Nazarov et al. (2009).3 Alexander et al. (2013).

Fig. 11. BSE images of Fe-rich veins in LEW 85311,31. (a) A vein enclosed within a narrow FGR. Most of the vein is close in chemicalcomposition to tochilinite. Relict kamacite (white) is indicated by an arrow. (b) A vein composed mainly of tochilinite and P-rich sulphide. Itwraps around a small chondrule fragment in a manner suggesting that its enclosing matrix has undergone ductile deformation.


The size distribution of LEW 85311 chondrules and chon-drule fragments can potentially provide valuable informa-tion about this meteorite’s relationship to carbonaceouschondrite groups. For example, chondrules in CV andCK meteorites have a larger apparent diameter than thosein COs and CMs (Friedrich et al., 2015). However, the onlydata on CM chondrule sizes that was available to Friedrich

et al. (2015) was an analysis of 100 chondrules in Murray,which have an average apparent diameter of 270± 240 lm (Rubin and Wasson, 1986). The size distributionof chondrules and chondrule fragments has recently beendetermined for Jbilet Winselwan (CM) (Friend et al.,2018). Two different lithologies were studied, whose chon-drules and chondrule fragments were of a similar apparent

Fig. 12. Chemical composition of LEW 85311,39 matrix andFGRs (atomic %). The 92 analyses (21 matrix, 71 FGR) all plotwithin the oval area, and average matrix and FGR values areshown. Also plotted is an analysis of cronstedtite and two analysesof type II TCI from the LEW 85311 matrix (analysed by STEM-EDX), and the bulk Mg/(Mg + Fe) ratio of LEW 85311 (Si notmeasured). The serpentine field is coloured green, and blacksquares are stoichiometric mineral compositions. Individual anal-yses are provided in the supplementary data.

Fig. 13. Images of LEW 85311,39 FGRs. (a) BSE image of the contact bThe FGR contains grains of Fe-sulphide (white) and micropores (black). (rich FGR. (c) HAADF STEM image showing a relatively large and intacand silicates (grey). Between these crystals are fine TCI fibres. (d) Bright-figrain surrounded by TCI fibres. (e) Interior of the enstatite (En) crystal iBright-field TEM image of a serpentine-rich area within a FGR.


size (141 lm and 149 lm in the two lithologies). Friendet al. (2018) suggested that the difference between JbiletWinselwan and Murray was because Rubin and Wasson(1986) did not measure chondrule fragments. The apparentdiameter of LEW 85311 chondrules and chondrule frag-ments (213 ± 153 lm) falls between Jbilet Winselwan andMurray, and is much smaller than the CVs and CKs. Inthe absence of a larger dataset of the size of CM chondrulesand chondrule fragments, the LEW 85311 measurementscannot be used to rigorously test the meteorite’s relation-ship to the CMs. FGRs in LEW 85311 have an averageapparent thickness of 37 lm, which is thinner than JbiletWinselwan (59–76 lm) (Friend et al., 2018). However, theslope of the correlation between chondrule apparent diam-eter and FGR apparent thickness is similar between the twometeorites, implying comparable conditions of rim forma-tion (LEW 85311 = 0.14; Jbilet Winselwan = 0.12–0.18)(Supplementary Fig. A3).

etween a FGR (lower right) and the enclosing matrix (upper left).b) BSE image of a type I chondrule that has a thick and micropore-t enstatite (En) crystal surrounded by grains of Fe-sulphide (white)eld TEM image of a similar field of view to (c) with an enstatite (En)n (c) and (d) showing a vein of poorly crystalline phyllosilicate. (f)

Fig. 14. Images of LEW 85311,39 matrix. (a) BSE image of a crystal of Ca-carbonate (Cc) that is rimmed by Fe-rich phyllosilicate (white). (b)BSE image of an area of matrix that contains �1 lm size objects with a rounded/bulbous shape that are analogous to GEMS particles; one ofthem is delineated by a dashed white line. Micropores (black) occur between the objects. (c) HAADF STEM image showing a mass of type IITCI crystals and a platy cronstedtite (Cron) crystal. The black area is porosity. (d) Bright-field TEM image of a different part of the samesample as (c), again with an intimate intergrowth of type II TCI and cronstedtite. The inset high-resolution TEM image shows the latticefringes of cronstedtite.

Table 9Chemical composition (atomic %) of cronstedtite and type-II TCI in the matrix of LEW 85311,39 compared with cronstedtite and tochilinitein type-II TCI from Paris (CM).

LEW 85311 Paris TCI

Cronstedtite TCI TCI Cronstedtite1 Tochilinite2

Si 9.1 ± 0.0 4.7 8.2 9.0 ± 0.8 1.0 ± 0.5Al 0.9 ± 0.1 1.3 3.2 1.0 ± 0.4 0.5 ± 0.3Fe 25.6 ± 0.7 26.4 23.5 21.3 ± 2.5 34.0 ± 2.5Ni – 0.9 0.4 n.a. n.a.Mg 1.1 ± 0.0 2.3 2.3 3.1 ± 1.5 2.3 ± 0.5S – 9.0 2.1 n.a. 19.3 ± 1.0O 63.5 ± 0.9 55.4 60.3 65.6 ± 1.7 42.5 ± 2.6

Total 100.0 100.0 100.0 100.0 99.6n 2 1 1 39 25

Analyses by TEM-EDX.The two analyses of LEW 85311 TCI chosen to illustrate the compositional range.n.a. – not analysed.± One standard deviation.Individual analyses for LEW 85311 provided in the supplementary data.1 Pignatelli et al. (2017, Table 3). Average of olivine- and pyroxene-hosted.2 Pignatelli et al. (2017, Table 2). Average of olivine- and pyroxene-hosted.


LEW 85311 refractory inclusions are similar in mineral-ogy to those that have been described from the CMs(Greenwood et al., 1994; Rubin, 2007). They are howeversmaller on average: 105 ± 88 lm in LEW 85311 versus130 ± 90 lm (n = 40) and 130 ± 80 lm (n = 37) for themildly altered CMs QUE 97,990 and Paris, respectively(Rubin, 2007, 2015). LEW 85311 refractory inclusions are

considerably more abundant than in the other two CMs(146/cm2 in LEW 85311 vs �80/cm2 in QUE 97990 and34/cm2 in Paris; Rubin, 2007, 2015). This high density ofrefractory inclusions is the most likely explanation forrefractory element and REEs composition of LEW 85311,which falls between Paris and the CVs (Fig. 1). As refrac-tory inclusions are 16O-rich, their unusually high concentra-


tion within LEW 85311 may also explain why its bulk oxy-gen isotopic composition plots within the CV-CO-CK field(Fig. 2). The difference between our analysis and the bulkmeasurement by Clayton and Mayeda (1999) may simplyreflect intra-meteorite heterogeneity in the abundance ofrefractory inclusions. The low degree of aqueous alterationand commensurately low volume of matrix of LEW 85311(Table 5) could also contribute to its bulk oxygen isotopiccomposition because the meteorite’s fine grained matrixhas a considerably higher d17O and d18O value than itschondrules and refractory inclusions (Clayton andMayeda, 1999; Fig. 2). The close similarity in volatile ele-ment compositions between LEW 85311 and Paris showsthat the two meteorites sample parent body regions thataccreted a similar range of volatile-bearing components,and that the nature of any fractionation during subsequentparent body processing was also comparable.

4.1.2. Agents of geological processing

By analogy with the CMs, post-accretionary processingof the LEW 85311 parent body could have included one ormore of: (i) shock metamorphism; (ii) brecciation; (iii)aqueous alteration; (iv) post-hydration heating (Brearley,2006). After falling to Earth the meteorite may also havebeen weathered (Lee and Bland, 2004). The S1 shock stageof LEW 85311 demonstrates that it has not experiencedpressures of >4–5 GPa (Stoffler et al., 1991) so that itslocalized and mild petrofabric can be explained by com-paction accompanying one or more low intensity impacts(e.g., Lindgren et al., 2015). None of the three thin sectionscontains clasts, thus showing that these impacts were suffi-ciently gentle that there was no brecciation or mixing (i.e.,deformation was ductile). The intact crystal structures oftochilinite and serpentine constrain the intensity of heatingthat LEW 85311 could have experienced after aqueousalteration. Estimates of the temperature at which tochilin-ite breaks down range from 120 �C (Zolensky et al., 1997)to 300 �C (Tonui et al., 2014), and serpentine starts todegrade at �300 �C (Akai, 1992). Kimura et al. (2011) usedmetal composition and sulphide texture to explore heatingof the CMs. They placed LEW 85311 in their group ‘‘A”,showing that it had not been significantly heatedbefore/during aqueous alteration, which would haveaffected the Fe, Ni metal, or after aqueous alteration,which would have been identifiable by the presence of pent-landite lamellae/blebs in pyrrhotite. This lack of evidencefor heating is also consistent with the unshocked andunbrecciated nature of LEW 85311 showing that it didnot experience high impact temperatures. We thereforeconclude that water-mediated alteration (parent bodyand/or terrestrial) was the main agent of post-accretionary processing of LEW 85311.

4.1.3. Mechanisms and products of aqueous alteration

The principal evidence for aqueous alteration of LEW85311 is the dissolution of some original components, andprecipitation of new phases (i.e., phyllosilicates, sulphides,carbonates). Here we evaluate the nature of the geochemi-cal reactions, the environments of water/rock interaction,and similarities to the CMs.

Dissolution of chondrule mesostasis glass has left porespaces between phenocrysts, whereas the relatively largeand rounded voids within chondrules may have formedby dissolution of Fe, Ni metal nuggets. The irregular/-faceted pores within FGRs were most likely produced bydissolution of one or more primary minerals (e.g., fayaliticolivine, metal, sulphide), and the greater abundance ofthese pores in outer parts of the rims may indicate that flu-ids responsible were hosted in the matrix. There is no evi-dence to determine the environment of chondrule andFGR dissolution (i.e., parent body, terrestrial or both).

Serpentine, cronstedtite, tochilinite and TCI were identi-fied by XRD and TEM, and are characteristic products ofCM parent body aqueous alteration (Bunch and Chang,1980; Barber, 1981; Mackinnon and Zolensky, 1984;Tomeoka and Buseck, 1985). Where they occur in thematrix and FGRs, these minerals are assumed to haveformed at the expense of fine-grained silicate, sulphideand metal, and probably also �1 lm size GEMS-like parti-cles. The absence of large TCI clumps distinguishes LEW85311 from the moderately to highly altered CMs (theycomprise 15–40 vol.% of CM2.2–2.6 meteorites (Rubinet al., 2007; Rubin 2015)). Evidence for replacement ofcoarser grained silicates by phyllosilicates is restricted tooccasional grains of fayalitic olivine and one crystal ofgehlenite. By contrast, nuggets and veins of kamacite havebeen extensively replaced by tochilinite, P-rich sulphide andschreibersite. Alteration of kamacite to sulphides was acommon reaction during the initial stages of aqueous pro-cessing of the CMs within geochemical environments witha high S activity (Tomeoka and Buseck, 1985; Palmer andLauretta, 2011). Overall, the processes and products ofaqueous alteration of LEW 85311 are closely comparableto ‘Stage 10 of the four-stage CM aqueous alterationsequence that was described by Hanowski and Brearley(2001) and refined by Velbel et al. (2012). Thus the geo-chemical environment within the LEW 85311 parent bodywas similar to the mildly altered CMs (i.e., pH, Eh,water/rock ratio, temperature).

By analogy with Antarctic ordinary chondrites(Buchwald and Clarke, 1989; Lee and Bland, 2004), theakaganeite-bearing mantles to kamacite grains are inter-preted to have formed by terrestrial weathering. Thus,LEW 85311 has been modified by reaction with water bothpre- and post-terrestrially, a combination of processes thatis common to the CM Elephant Moraine (EET) 96029 (Leeet al., 2016), and probably many other Antarctic carbona-ceous chondrites.

4.1.3.1. Ca-carbonate. Ca-carbonate is rare in LEW 85311.It was not detected by XRD, and Alexander et al. (2015)recorded 0.3 wt.% carbonate-hosted carbon in bulk samplesof both LEW 85311 and LEW 85312; this value is lowerthan 42 of the 43 unheated CMs analysed by Alexanderet al. (2015). Ca-carbonate occurs in three contexts: (i)within a gehlenite-bearing refractory inclusion (Fig. 8d);(ii) scarce small crystals within the matrix (Fig. 14a); (iii)meshworks of needle-fibre calcite (Figs. 9 and 10). By anal-ogy with calcite in refractory inclusions from the CM fallsMurchison (Armstrong et al., 1982) and Murray (Lee and


Greenwood, 1994), Ca-carbonate in the LEW 85311 refrac-tory inclusion is interpreted to have formed by parent bodyaqueous alteration. This conclusion is consistent withexperimental results showing that gehlenite alters to calcitewhen it reacts with carbonate-rich solutions underhydrothermal conditions (Nomura and Miyamoto, 1998).As the matrix-hosted Ca-carbonate has been partiallyreplaced by phyllosilicates, in common with calcite in thematrices of CM falls (Lee et al., 2014), it is likewise inter-preted to be the product of parent body processing.

Needle-fibre calcite could have formed on the parentbody or by terrestrial weathering, and these two environ-ments can be distinguished using its C and O isotopic com-position. Given that the needle-fibre calcite is by far themost abundant type of Ca-carbonate in each of the threeLEW 85311 thin sections, its isotopic composition shouldbe close to that of bulk Ca-carbonate in LEW 85311(d18O 19.4 ± 0.9‰, d13C 28.6 ± 0.2‰) and LEW 85312(d18O 23.0 ± 0.3‰, d13C 34.1 ± 0.2‰) (Alexander et al.,2015). In Supplementary Fig. A4 these values are plottedalong with the 43 CMs in Alexander et al. (2015), terrestrialcalcite in an Antarctic CM (d18O �9‰, d13C �0‰; Tyraet al., 2007), and terrestrial Ca-carbonate from Antarcticordinary chondrites (d18O 3–30‰, d13C = �6‰; Evanset al., 2017). The carbon isotopic composition of bulkLEW 85311 and LEW 85312 Ca-carbonate is very differentto the Antarctic weathering products, and so the needle-fibre calcite is interpreted to have formed on the LEW85311 parent body. The LEW 85311 and 85312 data plottowards the low d13C and d18O end of the trend definedby the CMs in Supplementary Fig. A4. Alexander et al.(2015) interpreted this trend to reflect differences in temper-ature of the carbonate-precipitating fluids (ranging from �0to 130 �C), thus implying that LEW 85311 and LEW 85312Ca-carbonate would have formed in the higher temperaturepart of the range.

Despite being isotopically consistent with the CMs,LEW 85311 needle-fibre calcite is distinct in its petro-graphic context, and crystal size and shape. CM calciteoccurs most commonly in the matrix as relatively coarseand equant grains, suggestive of slow rates of crystalgrowth from fluids of a low degree of supersaturation(Johnson and Prinz, 1993; de Leuw et al., 2010; Lee et al.,2014). Conversely, the small size of the needle-fibre crystalsand their random orientations relative to each other implyrapid crystal growth from highly supersaturated solutions.Terrestrial calcite that is very similar in crystal size andshape is termed ‘moonmilk’; it occurs in caves and burialtombs and forms by evaporation (Cirigliano et al., 2018;Spotl, 2018; Lee et al., 2019a,b). We therefore propose thatLEW 85311 needle-fibre calcite is also a parent body evap-orite. The consistent association of needle-fibre calcite withkamacite and its alteration products (P-rich sulphide,Fe-sulphide, schreibersite, tochilinite, eskolaite) suggeststhat the metal was aqueously altered prior to carbonate pre-cipitation, making space for the calcite. These kamacitegrains must have been relatively large (up to several hun-dred micrometres in diameter) and free-floating in the solarnebular so that they accreted FGRs (Hanna and Ketcham,2018). Most of the calcite-rich objects are rounded

(Fig. 10), but several have a shard-like shape (Fig. 9e) sug-gestive of brittle breakage of kamacite prior to accretion ofthe FGR. The geochemical conditions under which kama-cite alteration would associate with calcite precipitationare unknown. However, the common intergrowth of calcitewith TCI in CM matrices (Tomeoka and Buseck, 1985; Leeet al., 2014) is evidence for a genetic link between carbonateand sulphide precipitation in carbonaceous chondrite par-ent bodies.

4.2. Degree of aqueous alteration

LEW 85311 has been mildly altered when assessed rela-tive to the mineralogical and geochemical criteria that areused for the CMs. Kimura et al. (2011) found that it hasa ‘‘low” degree of aqueous alteration. LEW 85311 and itspair LEW 85312 have been assigned to petrologic typesof 1.9/1.8 (Alexander et al., 2013) and 1.7 (from XRD datain Table 4) (Table 1). Relative to the petrologic subtypes ofRubin et al. (2007), LEW has been tentatively assigned toCM2.6–2.7 (Choe et al., 2010) and to CM2.3 (Friedrichet al., 2018). These two different subtype assignments canbe tested by comparison with the petrologic types ofLEW 85311. There is a good linear correlation betweenthe three classification schemes for meteorites of petrologicsubtypes 2.0–2.6. (Supplementary Fig. A5). However, asthere are no meteorites have been classified at CM2.7 orhigher on the Rubin et al. (2007) scheme that have alsobeen measured by Alexander et al. (2013) or Howardet al. (2015), the nature of the correlation lines at lowerdegrees of aqueous alteration cannot be determined.Nonetheless, as a petrologic subtype of 3.0 on the Rubinet al. (2007) scale should equal a petrologic type of 3.0 onthe other two scales, the regression lines in SupplementaryFig. A5 can be extrapolated between CM2.6 and CM3.0.Using these lines, a petrologic type of 1.9–1.8 correspondsto �CM2.7–CM2.6, and 1.7 corresponds to �CM2.6 (Sup-plementary Fig. A5). Taking the two comparisons togethersuggests a subtype of CM2.7–CM2.6 for LEW 85311, inagreement with Choe et al. (2010).

It is difficult to assign LEW 85311 to a petrologic sub-type directly because the meteorite lacks large ‘‘PCPclumps”, whose abundance and chemical composition arekey metrics in the Rubin et al. (2007) scheme. The other cri-teria of Rubin et al. (2007) are consistent with a subtype ofCM2.6 or higher for LEW 85311 apart for the abundanceof Fe, Ni metal. They propose that meteorites of subtypeCM2.5 and CM2.6 should contain 0.03–0.3 vol.% and�1 vol.% metallic Fe-Ni, respectively. As XRD shows thatLEW 85311 contains 0.3 vol.% metal, a �CM2.5 classifica-tion is suggested. However, the only meteorite classified byRubin et al. (2007) as CM2.6 was QUE 97990, which con-tains 0.2 vol.% Fe,Ni metal as quantified by XRD (Howardet al. 2015). Furthermore, the 0.3 vol.% Fe,Ni metal isequal to its abundance in EET 96029 (a heated CM2.7;Lee et al., 2016), and only one of the 36 CMs plotted inFig. 3 is richer in metal. Therefore by using XRD-determined metal abundance alone, LEW 85311 is lessaltered than QUE 97,990 and so should be assigned to asubtype of CM2.6 or higher. The lack of chondrule glass


that is preserved in EET 96029 (CM2.7) and Paris (CM2.7;Marrocchi et al., 2014, Rubin 2015) argues against LEW85311 being significantly more pristine than these twoCMs, and so we conclude overall that it has a petrologicsubtype of CM2.7.

A variety of other properties of LEW 85311 are compa-rable to those of the most weakly aqueously altered CMs,which further demonstrates that LEW 85311 evolved in acomparable manner. Mild alteration is consistent with thepreservation of gehlenite, which is highly reactive in thepresence of liquid water (e.g., Rubin, 2007). LEW 85311has a low phyllosilicate fraction (Table 4), showing thatalteration stopped early (i.e., Stage 1 of Hanowski andBrearley, 2001) thereby preserving much of the original oli-vine and pyroxene. XRD also shows a high ratio of cronst-edtite to Mg,Fe serpentine. Little of the early formedcronstedtite had recrystallized to Mg-serpentine becausethe main sources of magnesium needed for this reactionare Mg-rich olivine and pyroxene, which are more resistantto parent body aqueous alteration than their Fe-rich equiv-alents (Tomeoka and Buseck, 1985; Tomeoka et al., 1989;Howard et al., 2009). The Mg/(Mg + Fe) of tochilinite afterkamacite in LEW 85311 is lower than the mildly alteredCMs Murchison and Murray (Table 7), again because rela-tively little Mg had been liberated from Mg-rich olivine andpyroxene that would otherwise have been available toincrease its Mg/(Mg + Fe) (Palmer and Lauretta, 2011).This limited supply of Mg during aqueous alteration is alsoexpressed by the MgO/FeO value of LEW 85311 matrix(0.33), which is significantly lower than that of Paris (0.39)(Supplementary Table A3). Finally, data in Nazarov et al.(2009) show a relationship between the chemical composi-tion of P-rich sulphides and degree of aqueous alterationof their host meteorite, and accordingly LEW 85311 P-richsulphides have a composition similar to those in the mostmildly altered CMs (Table 8). Therefore, multiple proxiesagree that LEW 85311 has been mildly altered, and its geo-chemical and mineralogical evolution followed a trajectoryclosely comparable to the most weakly hydrated CMs.

4.3. Affinity of LEW 85311

This meteorite has many similarities to the CMs, butalso some important differences that have prompted us toquestion its link to the group. The CMs are homogeneousin chemical composition (Rubin et al., 2007; Braukmulleret al., 2018; Friedrich et al., 2018), with any small differ-ences between meteorites being potentially attributable toterrestrial weathering (Friedrich et al., 2018). This composi-tional homogeneity has been interpreted to demonstratethat the CM3 starting material was chemically uniformand aqueous alteration was isochemical (i.e., closed aque-ous system) so that water-soluble elements (e.g., Na, K)were not leached (e.g., Brearley, 2006; Rubin et al., 2007;Bland et al., 2009; Velbel et al., 2012; Braukmuller et al.,2018; Friedrich et al., 2018). Rubin et al. (2007) concludedthat the compositional homogeneity of the CMs indicates asingle parent body for the group.

LEW 85311 sits outside of the narrow range of CMchemical compositions (i.e., principally in its refractory

elements and REEs; Fig. 1). We contend that this diver-gence from the CMs is due to a different starting material(i.e., one rich in refractory inclusions) that was isochemi-cally altered. An alternative explanation is that this mete-orite was initially chemically similar to other CMs butchanged in composition during open system aqueous alter-ation. However, in such a scenario LEW 85311 would beexpected to differ from the CMs in its water-soluble ele-ments rather than the most highly refractory elements asis observed (Fig. 1). Moreover, Mg should have been selec-tively leached, yet the chemical compositions of Mg-bearingalteration products (e.g., matrix and FGR phyllosilicatesand tochilinite) are consistent with mildly altered CMs.The oxygen isotopic compositions of the CMs are quitevariable, in part due to contrasting degrees of aqueousalteration and in a few cases also post-hydration heating(Clayton and Mayeda, 1999). LEW 85311 falls outside ofthe CM range (Fig. 2), but its unusual isotope values canagain be explained by abundant refractory inclusions.

LEW 85311 is almost indistinguishable from the mildlyaltered CMs with regards to the processes and productsof aqueous alteration (i.e., alteration of kamacite, sulphide,amorphous silicates and the most reactive silicate mineralsto cronstedtite, serpentine and sulphides). These alterationproducts also include tochilinite, which is a mineralogical‘hallmark’ of the CMs. The only evidence for a differencein alteration between LEW 85311 and the CMs is the pres-ence of needle-fibre calcite, which may have formed byevaporation of relatively high temperature parent body flu-ids, and the absence from the matrix of TCI ‘clumps’.Despite these differences, LEW 85311 is interpreted to haveoriginally contained a similar proportion of water ice tomany of the CMs, then was heated and remained warmfor a sufficient length of time to be mildly aqueouslyaltered.

NWA 5958 is a hydrated carbonaceous chondrite withsome similarities to LEW 85311. It has been classified asC2-ung and its bulk oxygen isotopic composition plotswithin the CV-CO-CK field close to one of the analysesof LEW 85311 (Jacquet et al., 2016) (Fig. 2). However thereis no petrographic or geochemical evidence for an elevatedabundance of refractory inclusions that could otherwiseaccount for this 16O-rich composition (Ash et al., 2011;Jacquet et al., 2016). Jacquet et al. (2016) found thatNWA 5958 is moderately aqueous altered relative to theCMs (�CM2.5 subtype), and its infra-red spectrum closelyresembles that of LEW 85311, especially in the 10 lmregion. The similarities between NWA 5958 and LEW85311 require further investigation, and one intriguing sug-gestion is that along with other ‘anomalous’ meteorites,NWA 5958 and LEW 85311 may be members of a newgroup of ‘primitive’ carbonaceous chondrites with CMaffinities (Greenwood et al., 2019).

We set out to ask whether LEW 85311 can provide newinsights into the diversity of hydrated C-complex meteoriteparent bodies. Our work has shown that the materialaccreted to form LEW 85311 was subtly different to theCMs, particularly with regards to the abundance of refrac-tory inclusions, yet this meteorite’s subsequent mineralogi-cal and geochemical evolution was very similar to other


members of the group. We therefore conclude that the CMclassification is appropriate, and that the diversity withinthe group shows that the CMs sample two or more parentbodies that accreted in a similar part of the solar nebula,and grew to a comparable size and at over a common time-scale (thus possessing a similar complement of short-livedradiogenic isotopes) so that they had an equivalent geolog-ical evolution. We anticipate that the forthcoming return ofsamples from the ‘rubble pile’ asteroids Ryugu (Watanabeet al., 2019) and Bennu (Lauretta et al., 2019) will greatlyenhance our understanding of the nature and diversity ofC-complex asteroids.

5. CONCLUSIONS

LEW 85311 is a CM carbonaceous chondrite, and mostof its properties are consistent with other members of thegroup. It is composed of rimmed chondrules, chondrulefragments and refractory inclusions supported within afine-grained matrix. The chondrules and chondrule frag-ments are similar in size to those of the CMs, although theirFGRs are relatively thin. LEW 85311 has undergone parentbody aqueous processing, and many of the alteration prod-ucts (e.g., serpentine, cronstedtite, tochilinite, P-rich sul-phide, TCI) are indistinguishable in mineralogy andchemical composition to those of the most mildly alteredCMs. However, there is evidence for a distinctive geochem-ical environment during aqueous alteration of LEW 85311from the presence of meshworks of needle-fibre calcitewithin objects that were previously rich in kamacite, andthe absence of TCI clumps. LEW 85311 is comparable tothe CMs in its volatile element composition, but differs inits refractory element, REE and bulk oxygen isotopic com-position owing to a high abundance of refractory inclu-sions. It also accreted an unusually low proportion ofwater ice, which limited the degree of aqueous alteration.LEW 85311 shows that the CM group samples more thanone parent body.

ACKNOWLEDGEMENTS

We thank Peter Chung for help with the SEM work, and aregrateful to ANSMET for providing the samples of LEW 85311.US Antarctic meteorite samples are recovered by the AntarcticSearch for Meteorites (ANSMET) program, which has beenfunded by NSF and NASA, and characterized and curated bythe Department of Mineral Sciences of the Smithsonian Institutionand Astromaterials Acquisition and Curation Office at NASAJohnson Space Center. This work was funded by the UK Scienceand Technology Facilities Council through grant ST/N000846/1.Author contributions: M.R.L. and B. E. C. designed the researchproject; M.R.L., B.E.C., A.J.K. and R.C.G. undertook analysesand contributed to writing and editing of the manuscript; M.R.L.acquired funding. We thank Alan Rubin and an anonymousreviewer for their helpful comments on the manuscript.

APPENDIX A. SUPPLEMENTARY MATERIAL

Supplementary data to this article can be found online athttps://doi.org/10.1016/j.gca.2019.07.027.

REFERENCES

Akai J. (1992) T-T–T diagram of serpentine and saponite, andestimation of metamorphic degree of Antarctic carbonaceouschondrites. Proc. Nat. Inst. Polar Res. Symp. Antarctic Mete-

orit. 5, 120–135.Alexander C. M. O’D., Bowden R., Fogel M. L., Howard K. T.,

Herd C. D. K. and Nittler L. R. (2012) The provenances ofasteroids, and their contributions to the volatile inventories ofthe terrestrial planets. Science 337, 721–723.

Alexander C. M. O’. D., Howard K. T., Bowden R. and Fogel M.L. (2013) The classification of CM and CR chondrites usingbulk H, C and N abundances and isotopic compositions.Geochim. Cosmochim. Acta 123, 244–260.

Alexander C. M. O’. D., Bowden R., Fogel M. L. and Howard K.T. (2015) Carbonate abundances and isotopic compositions inchondrites. Meteorit. Planet. Sci. 50, 810–833.

Alexander C. M. O’. D., Greenwood R. C., Bowden R., Gibson J.M., Howard K. T. and Franchi I. A. (2018) A multi-techniquesearch for the most primitive CO chondrites. Geochim. Cos-

mochim. Acta 221, 406–420.Armstrong J. T., Meeker G. P., Huneke J. C. and Wasserburg G. J.

(1982) The Blue Angel: I. the mineralogy and petrogenesis of ahibonite inclusion from the Murchison meteorite. Geochim.

Cosmochim. Acta 46, 575–595.Ash R. D., Walker R. J., Puchtel I. S., McDonough W. F. and

Irving A. J. (2011) The trace element chemistry of NorthwestAfrica 5958, a curious primitive carbonaceous chondrite(abstract #2325). 42nd Lunar and Planetary Science Conference.

Barber D. J. (1981) Matrix phyllosilicates and associated mineralsin C2M carbonaceous chondrites. Geochim. Cosmochim. Acta

45, 945–970.Bland P. A., Jackson M. D., Coker R. F., Cohen B. A., Webber J.

B. W., Lee M. R., Duffy C. M., Chater R. J., Ardakani M. G.,McPhail D. S., McComb D. W. and Benedix G. K. (2009) Whyaqueous alteration in asteroids was isochemical: high porosity– high permeability. Earth Planet. Sci. Lett. 287, 559–568.

Braukmuller N., Wombacher F., Hezel Dominik C., Escoube R.and Munker C. (2018) The chemical composition of carbona-ceous chondrites: Implications for volatile element depletion,complementarity and alteration. Geochim. Cosmochim. Acta

239, 17–48.Brearley A. J. (2006) The action of water. In Meteorites and the

Early Solar System II (eds. D. S. Lauretta, H. Y. McSween, D.S. Lauretta and H. Y. McSween). University of Arizona Press,pp. 587–624.

Buchwald V. F. and Clarke Jr R. S. (1989) Corrosion of Fe-Nialloys by Cl-containing akaganeite (b-FeOOH): The Antarcticmeteorite case. Am. Mineral. 74, 656–667.

Bunch T. E. and Chang S. (1980) Carbonaceous chondrites – II.Carbonaceous chondrite phyllosilicates and light element geo-chemistry as indicators of parent body processes and surfaceconditions. Geochim. Cosmochim. Acta 44, 1543–1577.

Burbine T. H. (2017) Asteroids: Astronomical and GeologicalBodies. Cambridge University Press, 367 pp.

Chizmadia L. J. and Brearley A. J. (2008) Mineralogy, aqueousalteration, and primitive textural characteristics of fine-grainedrims in the Y-791198 CMS carbonaceous chondrite: TEMobservations and comparison to ALHA81002. Geochim. Cos-

mochim. Acta 72, 602–625.Choe W. H., Huber H., Rubin A. E., Kallemeyn G. W. and

Wasson J. T. (2010) Compositions and taxonomy of 15 unusualcarbonaceous chondrites. Meteorit. Planet. Sci. 45, 531–554.

Cirigliano A., Tomassetti M. C., Di Pietro M., Mura F., ManeschiM. L., Gentili M. D., Cardazzo B., Arrighi C., Mazzoni C.,Negri R. and Rinaldi T. (2018) Calcite moonmilk of microbial


http://refhub.elsevier.com/S0016-7037(19)30451-X/h0005

































































origin in the Etruscan Tomba degli Scudi in Tarquinia, Italy.Sci. Rep. 8, 15839.

Clayton R. N. and Mayeda T. K. (1999) Oxygen isotope studies ofcarbonaceous chondrites. Geochim. Cosmochim. Acta 63, 2089–2104.

Cloutis E. A., Hudon P., Hiroi T., Gaffey M. J. and Mann P.(2011) Spectral reflectance properties of carbonaceous chon-drites: 2. CM chondrites. Icarus 216, 309–346.

de Leuw S., Rubin A. E., Schmidt A. K. and Wasson J. T. (2010)Carbonates in CM chondrites: complex formational historiesand comparison to carbonates in CI chondrites. Meteorit.

Planet. Sci. 45, 513–530.DeMeo F. E., Binzel R. P., Slivan S. M. and Bus S. J. (2009) An

extension of the Bus asteroid taxonomy into the near-infrared.Icarus 202, 160–180.

Evans M. E., Niles P. B., Locke D. R. and Chapman P. (2017)Isotopic composition of carbonates in Antarctic ordinarychondrites and Miller Range nakhlites: Insights into MartianAmazonian aqueous alteration. Lunar Planet. Sci., L#2727,(abstr.).

Friedrich J. M., Abreu N. M., Wolf S. F., Troiano J. M. andStanek G. L. (2018) Redox-influenced trace element composi-tional differences among variably aqueously altered CM chon-drites. Geochim. Cosmochim. Acta 237, 1–17.

Friedrich J. M., Weisberg Michael K., Ebel Denton S., Biltz A. E.,Corbett B. M., Iotzov I. V., Khan W. S. and Wolman M. D.(2015) Chondrule size and related physical properties: acompilation and evaluation of current data across all meteoritegroups. Chem. Erde 75, 419–443.

Friend P., Hezel D. C., Barrat J.-A., Zipfel J., Palme H. andMetzler K. (2018) Composition, petrology, and chondrule-matrix complementarity of the recently discovered JbiletWinselwan CM2 chondrite. Meteorit. Planet. Sci. 53, 2470–2491.

Greenwood R. C., Lee M. R., Hutchison R. and Barber D. J.(1994) Formation and alteration of CAIs in Cold Bokkeveld(CM2). Geochim. Cosmochim. Acta 58, 1913–1935.

Greenwood R. C., Burbine T. H. and Franchi I. A. (2019) Linkingasteroids and meteorites to the primordial parent body popu-lation: an oxygen isotope perspective. Geochim. Cosmochim.

Acta (in review).Greenwood R. C., Franchi I. A., Kearsley A. T. and Alard O.

(2010) The relationship between CK and CV chondrites.Geochim. Cosmochim. Acta 74, 1684–1705.

Greenwood R. C., Burbine T. H., Miller M. F. and Franchi I. A.(2017) Melting and differentiation of early-formed asteroids: theperspective from high precision oxygen isotope studies. Chemie

der Erde – Geochem. 77, 1–43.Grossman J. N. (1994) The Meteoritical Bulletin, no. 76, 1994

January: The U.S. Antarctic Meteorite Collection. Meteoritics

29, 100–143.Hamilton V. E., Simon A. A., Christensen P. R., Reuter D. C.,

Clark B. E., Barucci M. A., Bowles N. E., Boynton W. V.,Brucato J. R., Cloutis E. A., Connolly H. C., DonaldsonHanna K. L., Emery J. P., Enos H. L., Fornasier S., Haberle C.W., Hanna R. D., Howell E. S., Kaplan H. H., Keller L. P.,Lantz C., Li J.-Y., Lim L. F., McCoy T. J., Merlin F., NolanM. C., Praet A., Rozitis B., Sandford S. A., Schrader D. L.,Thomas C. A., Zou X.-D. and Lauretta D. S. (2019) OSIRIS-REx Team Evidence for widespread hydrated minerals onasteroid (101955) Bennu. Nat. Astron 3, 332–340.

Hanna R. D., Ketcham R. A., Zolensky M. and Behr W. M. (2015)Impact-induced brittle deformation, porosity loss, and aqueousalteration in the Murchison CM chondrite. Geochim. Cos-

mochim. Acta 171, 256–282.

Hanna R. D. and Ketcham R. A. (2018) Evidence for accretion offine-grained rims in a turbulent nebula for CM Murchison.Earth Planet Sci Lett. 481, 201–211.

Hanowski N. P. and Brearley A. J. (2001) Aqueous alteration ofchondrules in the CM carbonaceous chondrite, Allan Hills81002: Implications for parent body alteration. Geochim.

Cosmochim. Acta 65, 495–518.Hewins R. H., Bourot-Denise M., Zanda B., Leroux H., Barrat J.-

A., Humayun M., Gopel C., Greenwood R. C., Franchi I. A.,Pont S., Lorand J.-P., Courne‘de C., Gattacceca J., Rochette P.,Kuga M., Marrocchi Y. and Marty B. (2014) The Parismeteorite, the least altered CM chondrite so far. Geochim.

Cosmochim. Acta 124, 190–222.Howard K. T., Benedix G. K., Bland P. A. and Cressey G. (2009)

Modal mineralogy of CM2 chondrites by X-ray diffraction(PSD-XRD). Part 1: total phyllosilicate abundance and thedegree of aqueous alteration. Geochim. Cosmochim. Acta 73,4576–4589.

Howard K. T., Benedix G. K., Bland P. A. and Cressey G. (2011)Modal mineralogy of CM chondrites by X-ray diffraction(PSD-XRD). Part 2: degree, nature and settings of aqueousalteration. Geochim. Cosmochim. Acta 75, 2735–2751.

Howard K. T., Alexander C. M., D. O’., Schrader D. L. and DylK. A. (2015) Classification of hydrous meteorites (CR, CM andC2 ungrouped) by phyllosilicate fraction: PSD-XRD modalmineralogy and planetesimal environments. Geochim. Cos-

mochim. Acta 149, 206–222.Jacquet E., Barrat J.-A., Beck P., Caste F., Gattacceca J., Sonzogni

C. and Gounelle M. (2016) Northwest Africa 5958: A weaklyaltered CM-related ungrouped chondrite, not a CI3. Meteorit.

Planet. Sci. 51, 851–869.Johnson C. A. and Prinz M. (1993) Carbonate compositions in CM

and CI chondrites, and implications for aqueous alteration.Geochim. Cosmochim. Acta 57, 2843–2852.

Kallemeyn G. W. and Wasson J. T. (1981) The compositionalclassification of chondrites—I, the carbonaceous chondritegroups. Geochim. Cosmochim. Acta 45, 1217–1230.

Kimura M., Grossman J. N. and Weisberg M. K. (2011) Fe-Nimetal and sulfide minerals in CM chondrites: An indicator forthermal history. Meteorit. Planet. Sci. 46, 431–442.

King A. J., Schofield P. F. and Russell S. S. (2017) Type 1 aqueousalteration in CM carbonaceous chondrites: implications for theevolution of water-rich asteroids. Meteorit. Planet. Sci. 52,1197–1215.

King A. J., Russell S. S., Schofield P. F., Humphreys-Williams E.R., Strekopytov S., Abernathy F. A. J., Verchovsky A. B. andGrady M. M. (2019) The alteration history of the JbiletWinselwan CM carbonaceous chondrite: an analogue for C-type asteroid sample return. Meteorit. Planet. Sci. 54, 521–543.

Kitazato K. et al. (2019) The surface composition of asteroid162173 Ryugu from Hayabusa2 near-infrared spectroscopy.Science 364, 272–275.

Lauretta D. S. et al. (2019) The unexpected surface of asteroid(101955) Bennu. Nature 568, 55–60.

Lee M. R. (1993) The petrography, mineralogy and origins ofcalcium sulphate within the Cold Bokkeveld CM carbonaceouschondrite. Meteoritics 28, 53–62.

Lee M. R. and Greenwood R. C. (1994) Alteration of calcium- andaluminium-rich inclusions (CAIs) in the Murray (CM2) car-bonaceous chondrite. Meteoritics 29, 780–790.

Lee M. R., Lindgren P. and Sofe M. R. (2014) Aragonite,breunnerite, calcite and dolomite in the CM carbonaceouschondrites: high fidelity recorders of progressive parent bodyaqueous alteration. Geochim. Cosmochim. Acta 144, 126–156.

Lee M. R., Lindgren P., King A. J., Greenwood R. C., Franchi I.A. and Sparkes R. (2016) Elephant Moraine 96029, a very





































































































































mildly aqueously altered and heated CM carbonaceous chon-drite: implications for the drivers of parent body processing.Geochim. Cosmochim. Acta 92, 148–169.

Lee M. R., Bland P. A. and Graham G. (2003) Preparation ofTEM samples by focused ion beam (FIB) techniques: applica-tions to the study of clays and phyllosilicates in meteorites.Min.

Mag. 67, 581–592.Lee M. R. and Bland P. A. (2004) Mechanisms of weathering of

meteorites recovered from hot and cold deserts and theformation of phyllosilicates. Geochim. Cosmochim. Acta 68,893–916.

Lee M. R., Cohen B. E., King A. J., Greenwood R. C. and GibsonJ. (2019a) Moonmilk in the carbonaceous chondrites. LunarPlanet. Sci. L#1367 (abstr.).

Lee M.R., Cohen B.E. and King A.J. (2019b) Alkali-halogenmetasomatism of Meteorite Hills 01075 (CM2) driven by shockheating: An analogue for Ryugu. 82nd Annual MeteoriticalSociety Meeting 6070.pdf.

Leroux H., Cuvillier P., Zanda B. and Hewins R. H. (2015) GEMS-like material in the matrix of the Paris meteorite and the earlystages of alteration of CM chondrites. Geochim. Cosmochim.

Acta 170, 247–265.Lindgren P., Hanna R. D., Dobson K. J., Tomkinson T. and Lee

M. R. (2015) The paradox between low shock-stage andevidence for compaction in CM carbonaceous chondritesexplained by multiple low-intensity impacts. Geochim. Cos-

mochim. Acta 148, 159–178.Lodders K. (2003) Solar system abundances and condensation

temperatures of the elements. Astrophys. J. 591, 1220–1247.Mackinnon I. D. R. and Zolensky M. E. (1984) Proposed

structures for poorly characterized phases in C2M carbona-ceous chondrite meteorites. Nature 309, 240–242.

Mahan B., Moynier F., Beck P., Pringle E. A. and Siebert J. (2018)A history of violence: Insights into post-accretionary heating incarbonaceous chondrites from volatile element abundances, Znisotopes and water contents. Geochim. Cosmochim. Acta 220,19–35.

Marrocchi Y., Gounelle M., Blanchard I., Caste F. and KearsleyA. T. (2014) The Paris meteorite: secondary minerals andasteroidal processing. Meteorit. Planet. Sci. 49, 1232–1249.

McSween, Jr., H. Y. (1979a) Are carbonaceous chondrites prim-itive or processed? Ann. Rev. Rev. Geophys. Space Phys. 17,1059–1078.

McSween, Jr., H. Y. (1979b) Alteration in CM carbonaceouschondrites inferred from modal and chemical variations inmatrix. Geochim. Cosmochim. Acta 43, 1761–1770.

McSween, Jr., H. Y. (1987) Aqueous alteration in carbonaceouschondrites: Mass balance constraints on matrix mineralogy.Geochim. Cosmochim. Acta 51, 2469–2477.

Metzler K., Bischoff A. and Stoffler D. (1992) Accretionary dustmantles in CM chondrites: evidence for solar nebula processes.Geochim. Cosmochim. Acta 56, 2873–2897.

Miller M. F., Franchi I. F., Sexton A. S. and Pillinger C. T. (1999)High precision D17O isotope measurements of oxygen fromsilicates and other oxides: methods and applications. Rapid

Commun. Mass Spectrom. 13, 1211–1217.Nazarov M. A., Kurat G., Brandstaetter F., Ntaflos T., Chaussi-

don M. and Hoppe P. (2009) Phosphorus-bearing sulfides andtheir associations in CM chondrites. Petrology 17, 101–123.

Nomura K. and Miyamoto M. (1998) Hydrothermal experimentson alteration of Ca-Al-rich inclusions (CAIs) in carbonaceouschondrites: implications for aqueous alteration in parentasteroids. Geochim. Cosmochim. Acta 62, 3575–3588.

Palguta J., Schubert G. and Travis B. J. (2010) Fluid flow andchemical alteration in carbonaceous chondrite parent bodies.Earth Planet. Sci. Lett. 296, 235–243.

Palmer E. E. and Lauretta D. S. (2011) Aqueous alteration ofkamacite in CM chondrites. Meteorit. Planet. Sci. 46, 1587–1607.

Pignatelli I., Marrocchi Y., Mugnaioli E., Bourdelle F. andGounelle M. (2017) Mineralogical, crystallographic and redoxfeatures of the earliest stages of fluid alteration in CMchondrites. Geochim. Cosmochim. Acta 209, 106–122.

Rubin A. E. (2007) Petrography of refractory inclusions in CM2.6QUE 97990 and the origin of melilite-free spinal inclusions inCM chondrites. Meteorit. Planet. Sci. 42, 1711–1729.

Rubin A. E. (2012) Collisional facilitation of aqueous alteration ofCM and CV carbonaceous chondrites. Geochim. Cosmochim.

Acta 90, 181–194.Rubin A. E. (2015) An American on Paris: extent of aqueous

alteration of a CM chondrite and the petrography of itsrefractory and amoeboid olivine inclusions. Meteorit. Planet.

Sci. 50, 1595–1612.Rubin A. E., Trigo-Rodriguez J. M., Huber H. and Wasson J. T.

(2007) Progressive aqueous alteration of CM carbonaceouschondrites. Geochim. Cosmochim. Acta 71, 2361–2382.

Rubin A. E. and Wasson J. T. (1986) Chondrules in the MurrayCM2 meteorite and compositional differences between CM-COand ordinary chondrite chondrules. Geochim. Cosmochim. Acta

50, 307–315.Schrader D. L., Davidson J., Greenwood R. C., Franchi I. A. and

Gibson J. M. (2014) A water-ice rich minor body from the earlySolar System: The CR chondrite parent body. Earth Planet Sci.

Lett. 407, 48–60.Scott E. R. D., Keil K. and Stoffler D. (1992) Shock metamorphism

of carbonaceous chondrites. Geochim. Cosmochim. Acta 56,4281–4293.

Sears D. W. G., Benoit P. H. and Jie L. (1993) Two chondrulegroups each with distinc-tive rims in Murchison recognized bycathodoluminescence. Meteoritics 28, 669–675.

Simon S. B., Keaton C. G. and Grossman L. (2005) Refractoryinclusions from the CM2 chondrite LEW85311. 68th Annual

Meteoritical Society Meeting (2005) 5122.pdf.Spotl C. (2018) Moonmilk as a human and veterinary medicine:

evidence of past artisan mining in caves of the Austrian Alps.Int. J. Speleol. 47, 127–135.

Starkey N. A., Jackson C. R. M., Greenwood R. C., Parman S.,Franchi I. A., Jackson M., Fitton J. G., Stuart F. M., Kurz M.and Larsen L. M. (2016) Triple oxygen isotopic composition ofhigh-3He/4He mantle. Geochim. Cosmochim. Acta 176, 227–238.

StofflerD., Keil K. and Scott E.R.D. (1991) Shockmetamorphismofordinary chondrites. Geochim. Cosmochim. Acta 55, 3845–3867.

Tomeoka K. and Buseck P. R. (1985) Indicators of aqueousalteration in CM carbonaceous chondrites: microtextures of alayered mineral containing Fe, S, O, and Ni. Geochim.

Cosmochim. Acta 49, 2149–2163.Tomeoka K., McSween H. Y. and Buseck P. R. (1989) Miner-

alogical alteration of CM chondrites: a review. Proc. Nat. Inst.

Polar Res. Symp. Antarctic Meteorit. 2, 221–234.Tonui E., Zolensky M., Hiroi T., Nakamura T., Lipschutz M.,

Wang M.-S. and Okudaira K. (2014) Petrographic, chemicaland spectroscopic evidence for thermal metamorphism incarbonaceous chondrites I: CI and CM chondrites. Geochim.

Cosmochim. Acta 126, 284–306.Trigo-Rodriguez J. M., Rubin A. E. and Wasson J. T. (2006) Non-

nebular origin of darkmantles around chondrules and inclusionsin CM chondrites. Geochim. Cosmochim. Acta 70, 1271–1290.

Tyra M. A., Farquhar J., Wing B. A., Benedix G. K., Jull A. J. T.,Jackson T. and Thiemens M. H. (2007) Terrestrial alteration ofcarbonate in a suite of Antarctic CM chondrites: evidence fromoxygen and carbon isotopes. Geochim. Cosmochim. Acta 71,782–795.








































































































































Velbel M. A., Tonui E. K. and Zolensky M. E. (2012) Replacementof olivine by serpentine in the carbonaceous chondrite Nogoya(CM2). Geochim Cosmochim. Acta 87, 117–135.

Watanabe S. et al. (2019) Hayabusa2 arrives at the carbonaceousasteroid 162173 Ryugu—a spinning top–shaped rubble pile.Science 364, 268–272.

Weisberg M. K., McCoy T. J. and Krot A. N. (2006) Systematicsand evaluation of meteorite classification. In Meteorites and the

Early Solar System II (eds. D. S. Lauretta, H. Y. McSween, D.S. Lauretta and H. Y. McSween). University of Arizona Press,Arizona, USA, pp. 19–52.

Xiao X. and Lipschutz M. E. (1992) Labile trace elements incarbonaceous chondrites: a survey. J. Geophys. Res. Planets 97,10199–10211.

Zolensky M. E., Mittlefehldt D. W., Lipschutz M. E., Wang M.-S.,Clayton R. N., Mayeda T. K., Grady M. M., Pillinger C. andBarber D. (1997) CM chondrites exhibit the complete petro-logic range from type 2 to 1. Geochim. Cosmochim. Acta 61,5099–5115.

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the diversity of cm carbonaceous chondrite parent bodies...

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